The present invention relates to an electrical circuit, and more particularly to a direct current electrical circuit having a smart wire harness capable of detecting arc faults.
An automotive industry need exists to increase the electrical power capability for future vehicles. In fact, the automotive industry plans to increase direct current systems from 14 volts to 42 volts. The driving forces contributing toward this change are the need to reduce fuel consumption and the introduction of new electrical features. New power networks must accommodate the increase energy demand of comfort and security devices as well as the electrical needs of major systems such as braking, electric power steering and suspension systems. The introduction of a system voltage higher than approximately 20 volts, defined herein as high system voltage, forces considerable component and system changes regarding reliability and electrical safety. More specifically, the impact of a forty-two volt direct current network on electrical distributions systems and components focuses primarily on the arcing phenomenon. A need exists to protect wire harnesses from unwanted arc faults, which may occur as a result of cut, pinched or chaffed wiring.
In the instance of a wire being cut or broken under an electrical load, an arc may be drawn between both ends. Such an arc is unwanted and unplanned for, and its extinction is uncertain. Therefore, severe damage may occur if the arc is sustained. This type of arc fault is called a series arc fault, as the arc is in series to the load. Hot unplugs due to vibrating loose connections fall into the same series arc fault category. Series arc faults cannot typically be cleared by fuses or circuit breakers.
Arc faults in parallel to the load are identified as parallel arc faults. An example of parallel arc faults can be damaged wires drawing an arc to a ground potential, such as a chassis of an automobile. The insulation jacket of such wires might be broken due to aging or shaved, chaffed or pinched cable jackets. This type of arc fault is usually created by a temporary short circuit. The arc fault current however may thermally over load and damage contacts within the circuit due to low contact force resulting in melting and evaporating contact material followed by more arcing. The arc fault current, limited by the circuit impedance and the arc voltage, can be significantly lower than the trip current of the protection device such as a fuse or circuit breaker, so that the fault is cleared late depending on the time or current characteristics or in some cases not at all.
A direct current electrical circuit having a smart wire harness has integrated electronics which measure both voltage and current through wires of the harness which are located substantially within a protection zone. The protection zone is disposed directly between two smart connectors which are wired in series via the wire harness to detect serial or parallel arc faults within the protection zone. To measure serial arc faults, a voltage is measured at each smart connector and a difference taken which equals the serial arc voltage. If this differential voltage increases to a preset value, a switching device which provides power to the smart wire harness is opened. To detect parallel arc faults, that is those arcs which jump between a positive wire and a ground wire of the wire harness, the current is measured at both ends of a positive wire of the smart wire harness via the same smart connectors. If the ending current is less than the beginning current, signaling a parallel arc due to the arc resistance to the arc itself, the same switching device is opened.
Preferably, the smart wire harness requires two signal wires to transfer the values of the end voltage and end current from the smart end connector to the first or the beginning smart connector. Depending upon the number of positive wires carried by the wire harness, a multiplexer can be used in the end smart connector and a demultiplexer can be used in the beginning smart connector to reduce the number of required signal wires.
Features and advantages of the present invention include a smart wire harness which can be used in a high voltage system. Another advantage of the present invention is a relatively inexpensive and robust wire harness capable of detecting both serial and parallel arc faults and capable of reacting to such faults to prevent further circuit damage.